A broad range of electronic systems employ power supplies with output voltages that can vary while the system is operating. Systems that operate with varying supply voltages from these power supplies include devices that reduce energy consumption at times when system functionality can be reduced. Computing systems often employ processors that can dynamically vary processing performance by, in part, operating at different voltage levels. “Sleep” or “standby” modes reduce power consumption, for example. Examples of such systems are laptop and desk top computers, servers, and battery powered mobile devices such as smartphones, netbook computers, mobile telephones, handheld games, and tablet computing devices. Systems other than computing devices may also have variable power supplies that reduce energy use and cost of operation in different modes of operation. The term “variable power supply” as used herein refers to power supplies with dynamically variable output voltage.
Devices that operate with variable power supplies often require that the output voltage transitions between different output voltage levels occur within a specified timeframe, and with little or no output voltage overshoot and/or undershoot. An under-damped voltage control loop of a power supply often results in rapid output voltage transitions, but may also cause excessive voltage overshoot and/or undershoot when transitioning between different output voltages. A power supply employing an over-damped voltage control loop may have little or no output voltage overshoot and undershoot, but excessive delays may occur when transitioning between output voltages.